1. Field of the Invention
This invention relates to a process for the production of trialkylsilyl (fluorosulfonyl)difluoroacetate by contacting (fluorosulfonyl)difluoroacetyl fluoride with siloxanes, preferably in the absence of carboxylate anion silylation catalyst. This invention further relates to reducing the amount of (fluorosulfonyl)difluoroacetic acid in the trialkylsilyl (fluorosulfonyl)difluoroacetate by contacting with trialkylsilyl halide.
2. Description of Related Art
Trialkylsilyl(fluorosulfonyl)difluoroacetate (FSO2CF2CO2SiR3, referred to herein as RSUTAS) is a precursor of difluorocarbene and is used for the cyclopropanation of olefins (see Dolbier, et al. in Journal of Fluorine Chemistry, Volume 125, pages 459 to 469 (2004)). This cyclopropanation has value in the pharmaceutical and agricultural chemical industries as a means for preparing commercially useful compounds.
Trimethylsilyl(fluorosulfonyl)difluoroacetate (RSUTMS) was originally prepared by the reaction of the silver salt of (fluorosulfonyl)difluoroacetic acid with trimethylsilyl iodide (Terjeson et al. in J. Fluorine Chem., Volume 42, pages 187 to 200 (1989)).
Tian et al. in Organic Letters, Volume 2, pages 563 to 564 (2000) describe a procedure for preparation of RSUTMS involving the reaction of (fluorosulfonyl)difluoroacetic acid (RSUA) with trimethylsilyl chloride. RSUTMS manufacturing procedures based on RSUA are not preferred because RSUA is derived from (fluorosulfonyl)difluoroacetyl fluoride
(RSU). Thus, when RSU (acid fluoride) is hydrolyzed to make RSUA (the acid), hydrogen fluoride (HF) is generated and must be disposed of. Then, when RSUA is reacted with trialkylsilyl halide (halotrialkylsilane), for example the chloride, hydrogen chloride is generated. Thus, this process generates stoichiometric quantities of HF and HCl.
Another problem with known methods for the production of RSUTAS is that the product is usually contaminated with (fluorosulfonyl)difluoroacetic acid (FSO2CF2CO2H, RSUA) as a by-product due to reaction of the RSU precursor and/or the trialkylsilyl ester product with adventitious water. The presence of RSUA in RSUTAS is deleterious to subsequent uses of this compound as a cyclopropanation reagent. The literature describes addition of triethylamine to RSUTMS to remove RSUA. Unfortunately, this procedure is difficult to control and can result in rapid decomposition of the entire sample.
Farnham in U.S. Pat. No. 5,268,511 teaches the preparation of trifluorovinyl ethers by reaction of a siloxane with hexafluoropropylene oxide-based carboxylic acid fluorides or anhydrides, optionally in the presence of a carboxylate anion silylation catalyst to provide useful reaction rates. The resulting silyl ester intermediate is converted to the trifluorovinyl ether by heating in the presence of a thermolysis catalyst. However, disclosure of Farnham is limited to carboxylic acid fluorides as a starting material which contain the group —O(C2F4)COF or —O(C2F4)—C(O)O(O)C(C2F4)O— and thus exclude RSU as a starting material. As discussed above, RSUTAS decomposes to form a difluorocarbene radical and cannot form a vinyl ether. Moreover, if it is attempted to produce RSUTAS employing a process step as in Farnham, i.e., reacting siloxane with RSU in the presence of carboxylate anion silylation catalyst, RSUTAS is not produced in significant yield.
A process is needed to make RSUTAS which reduces or eliminates the significant production of unwanted by-products such as HF. In addition, it is desirable to reduce the RSUA by-product.